In current video and file delivery solutions, almost all mobile operators support and use a unicast mode of delivering files to users. Unicast is the sending of data to a single network destination identified by a unique address. Unicast is triggered by the end user when a data file is required, and the file delivery from a server node occupies dedicated radio resources. Such a network is shown in FIG. 1a, where a server node 101 (or sender) transmits data files to user equipment nodes (or receivers) 1031 to 103N, via one or more intermediate nodes 105. As can be seen, files are delivered in unicast mode, such that the same file being transmitted to user equipment nodes 1031 and 1032 results in the same file being delivered twice, in parallel, between certain nodes. In the mobile network, the radio resource is limited and depending upon demand, the support for users is limited, and end user quality of experience cannot always be guaranteed.
Multimedia Broadcast/Multicast Service (MBMS) is a Point-to-Multipoint (PtM) service offered via cellular networks which overcomes the limitations of unicast file delivery, and opens up opportunities for operators to off-load premium content and file delivery to mobile and fixed devices in geographic locations. Such a solution is shown in FIG. 1b, where a file is delivered in a point-to-multipoint manner between a server node 101 and one or more user equipment nodes or receivers 1031 to 103N.
Evolved MBMS (eMBMS) is used to denominate an eMBMS service in the Evolved Packet Core (EPC) Solution including evolved UMTS Terrestrial Radio Access Network (e-UTRAN) and UTRAN Access.
MBMS download can be used to deliver an arbitrary number of files from a single source to many receivers. MBMS download typically makes use of the File Transport over Unidirectional Transport protocol (FLUTE, RFC3926), for file delivery. FLUTE is designed for massive file delivery over unidirectional links such as those used for digital broadcasts.
The purpose of a file repair procedure is to repair lost or corrupted file fragments from the MBMS download data transmission.
The technical specification of the 3rd Generation Partnership Project (3GPP) relating to RFC 26.346, entitled “Multimedia Broadcast/Multicast Service (MBMS); Protocols and codecs” has defined a point-to-point (PtP) file repair procedure, and mechanisms to prevent a flood of file repair requests from user equipment nodes.
FIG. 2 illustrates a scheme defined in RFC 26.346, whereby after transmission of a file has been completed, there exists a back-off time 201 before user equipment nodes can request a file repair procedure using signals 203, 205, that communicate between a user equipment node and a file repair server 207, these back-off times being randomly selected for different user equipment nodes, such that a flood of point-to-point file repair requests are not sent at the same time.
Although this random distribution of file repair requests helps prevent system failure due to overload, the mechanism still has the disadvantage of being an inefficient way of processing file repair requests.